202 million km (1.35 AU or 125 million miles) from Earth an explorer from Earth is investigating the giant asteroid Vesta. This intrepid pioneer is the Dawn space probe.
Orbiting about 2700 km (1700 miles) above Vesta, Dawn slowly rotates around the world beneath it. Every 69 hours, the spacecraft completes a circuit (meanwhile Vesta is rotating beneath, a day there is only five hours 20 minutes long). As Dawn follows its course, it passes north to south over the asteroid’s poles. As it passes over the dayside the spacecraft observes the illuminated surface, recording what it sees, then on the other half of its orbit as it passes over the nightside, the robotic explorer transmits its findings to distant Earth. Data transmitted by radio from Dawn takes 11 minutes to reach home.
NASA has just released a fascinating new animation showing the whole asteroid as it rotates beneath Dawn.
The Dawn spacecraft will continue orbiting the giant asteroid for a year, before departing for the dwarf planet Ceres. Dawn will reach Ceres in 2015, revealing the mysteries of its icy surface.